The last CL https://chromium-review.googlesource.com/c/456707/ caused
some pretty heavy performance regressions. After experimenting, it
seems the easiest and most straight-forward way to copy the elements
into the new typed array is to do it in JS.
Adds a fast path for typed arrays, where the source typed array has
the same elements kind, in which case we can just copy the backing
store using memcpy.
This CL also removes regression test 319120 which is from a pwn2own
vulnerability. The old code path enforced a maximum byte_length
that was too low, which this change removes. The length property of
the typed array must be a Smi, but the byte_length, which can be up
to 8x larger than length for a Float64Array, can be a heap number.
We can also re-use some of the logic from ConstructByLength when
deciding whether to allocate the buffer on- or off-heap, so that
is factored out into InitializeBasedOnLength. We can also re-use
the DoInitialize helper instead of calling into the runtime,
meaning we can remove InitializeFromArrayLike.
BUG=v8:5977,chromium:705503,chromium:705394
Change-Id: I63372652091d4bdf3a9491acef9b4e3ac793a755
Reviewed-on: https://chromium-review.googlesource.com/459621
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44301}
a450c18544